In the substrates for plastic lenses, particularly transparent substrates reflect beams of light from the sun or the illumination and suffer from loss of transmittance of light. Owing to this loss of transmittance, a light passed through a lens loses in brightness. The reflection of light produces a reflected image called a ghost on the lens surface and imparts an unpleasant feeling to the eyes of the person wearing the lens. In the plastic substrates, the eyeglass lens is deficient in surface hardness and liable to sustain scratches. For the alleviation of the impacts of these drawbacks, the practice of coating the eyeglass lens with a film, particularly an antireflection film, of an organic substance by vacuum evaporation is in vogue.
When the antireflection film is covered with electrostatically deposited dirt and dust or with physically deposited filth, fingerprints, and perspiration from hands, it is misted possibly to the extent of obstructing the vision of the person wearing the eyeglass and compelling the person to experience an unpleasant feeling. In the circumstances, wiping cloth and paper and detergents useful for temporary removal of dirt are offered in the market. Methods for imparting a dirtproofing property to the antireflection film by applying a substance containing an organic silicon compounds on the film have been disclosed in Japanese Patent Application Disclosures SHO 61(1981)-130,902, SHO 51(1976)-1,387, and SHO 50(1975)-10,440, for example. The conventional methods effect the surface treatment by employing the dip coating method and attain the drying of a wet applied layer by allowing the wet layer to stand overnight at normal room temperature or to stand for not less than 20 minutes at a temperature of about 100.degree. C. Thus, they invariably require the wet applied layer to be dried by standing either for a long time or at an elevated temperature.
The conventional dirtproofing treatment of a lens resorting to the dip coating method has a disadvantage that the film formed by vacuum evaporation is liable to sustain cracks in the surface, through which the lens suffer from impairment of its appearance, because the wet applied film has to be dried by a protracted standing at an elevated temperature approximately in the range of 50.degree. C. to 70.degree. C. or by a brief standing at higher temperature approximately in the range of 70.degree. C. to 100.degree. C. The protracted standing for the purpose of drying is nothing desirable from the standpoint of productivity.
The dip coating method is popularly used for the treatment under discussion. The conventional dip coating method has a disadvantage that the applied liquid layer tends to leave a mark of drawdown on the lens surface and form a dry layer of uneven wall thickness. If the drawdown blurs the lens surface, the mark of blur stands out and spoils the appearance of the lens.
The polyfluoroalkyl silane which is used as an organic silicon comound for the dirtproofing treatment is so expensive that generous use of this compound is undesirable from the standpoint of cost.